/* display.c - The display component of a virtual console.
   Copyright (C) 2002 Free Software Foundation, Inc.
   Written by Marcus Brinkmann and Kalle Olavi Niemitalo.

   This file is part of the GNU Hurd.

   The GNU Hurd is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2, or (at
   your option) any later version.

   The GNU Hurd is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA. */

#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <wchar.h>
#include <iconv.h>
#include <argp.h>
#include <string.h>

#include <sys/io.h>
#include <sys/mman.h>
#include <sys/fcntl.h>
#include <cthreads.h>

#ifndef __STDC_ISO_10646__
#error It is required that wchar_t is UCS-4.
#endif

#include "display.h"


struct screen
{
  /* A screen matrix, including the scroll back buffer.  */
  wchar_t *matrix;

  /* The size of the screen, in lines.  */
  int lines;

  /* The top most line of the screen in the video buffer.  */
  int current_line;

  /* Maximum number of lines scrolled back.  */
  int scrolling_max;

  int width;
  int height;
};
typedef struct screen *screen_t;

struct cursor
{
  /* The visibility of the cursor.  */
  u_int32_t status;
#define CURSOR_INVISIBLE 1
#define CURSOR_STANDOUT 2

  u_int32_t x;
  u_int32_t y;
  u_int32_t saved_x;
  u_int32_t saved_y;
};
typedef struct cursor *cursor_t;

struct parse
{
  /* The parsing state of output characters, needed to handle escape
     character sequences.  */
  enum
    {
      STATE_NORMAL = 0,
      /* An escape character has just been parsed.  */
      STATE_ESC,
      STATE_ESC_BRACKET_INIT,
      STATE_ESC_BRACKET,
      STATE_ESC_BRACKET_QUESTION
    } state;

  /* How many parameters an escape sequence may have.  */
#define PARSE_MAX_PARAMS 10
  int params[PARSE_MAX_PARAMS];
  int nparams;
};
typedef struct parse *parse_t;

struct output
{
  /* The state of the conversion of output characters.  */
  iconv_t cd;
  /* The output queue holds the characters that are to be outputted.
     The conversion routine might refuse to handle some incomplete
     multi-byte or composed character at the end of the buffer, so we
     have to keep them around.  */
  int stopped;
  struct condition resumed;
  char *buffer;
  size_t allocated;
  size_t size;

  /* The parsing state of output characters.  */
  struct parse parse;
};
typedef struct output *output_t;

struct attr
{
  /* Current attribute.  */
  char current;
  int fg;
  int bg;
  int def_fg;
  int def_bg;
  int reverse : 1;
  int bold : 1;
  int blink : 1;
  int invisible : 1;
  int dim : 1;
  int underline : 1;
};
typedef struct attr *attr_t;

struct display
{
  /* The lock for the virtual console display structure.  */
  struct mutex lock;

  struct screen screen;
  struct cursor cursor;
  struct output output;
  struct attr attr;

  /* Indicates if OWNER_ID is initialized.  */
  int has_owner;
  /* Specifies the ID of the process that should receive the WINCH
     signal for this virtual console.  */
  int owner_id;
};


static error_t
screen_init (screen_t screen)
{
  screen->width = 80;
  screen->height = 25;
  screen->lines = 25;	/* XXX For now.  */
  screen->current_line = 0;
  screen->matrix = calloc (screen->lines * screen->width, sizeof (wchar_t));
  if (!screen->matrix)
    return ENOMEM;

  wmemset (screen->matrix, L' ', screen->height * screen->width);
  /* XXX Set attribute flags.  */
  return 0;
}

static void
screen_deinit (screen_t screen)
{
  free (screen->matrix);
}

static void
screen_fill (screen_t screen, size_t x, size_t y, size_t w, size_t h,
	     wchar_t chr, char attr)
{
  wchar_t *matrixp = screen->matrix
    + ((screen->current_line + y) % screen->height) * screen->width + x;

  while (h--)
    {
      /* XXX Set attribute flags.  */
      wmemset (matrixp, L' ', w);
      matrixp += screen->width;
    }

  /* XXX Flag screen change, but here?  */
}

static void
screen_scroll_up (screen_t screen, size_t x, size_t y, size_t w, size_t h,
		  int amt, wchar_t chr, char attr)
{
  wchar_t *matrixp = screen->matrix
    + ((screen->current_line + y) % screen->height) * screen->width + x;

  if (amt < 0)
    return;

  while (h-- > amt)
    {
      wmemcpy (matrixp, matrixp + amt * screen->width, w);
      matrixp += screen->width;
    }
  screen_fill (screen, x, y, w, h, chr, attr);
}

static void
screen_scroll_down (screen_t screen, size_t x, size_t y, size_t w, size_t h,
		    int amt, wchar_t chr, char attr)
{
  wchar_t *matrixp = screen->matrix
    + ((screen->current_line + y + h - 1) % screen->height)
    * screen->width + x;

  if (amt < 0)
    return;

  while (h-- > amt)
    {
      wmemcpy (matrixp, matrixp - amt * screen->width, w);
      matrixp -= screen->width;
    }
  screen_fill (screen, x, y, w, h, chr, attr);
}

static void
screen_scroll_left (screen_t screen, size_t x, size_t y, size_t w, size_t h,
		    int amt, wchar_t chr, char attr)
{
  int i;
  wchar_t *matrixp = screen->matrix
    + ((screen->current_line + y) % screen->height) * screen->width + x;

  if (amt < 0)
    return;
  if (amt > w)
    amt = w;

  for (i = 0; i < y + h; i++)
    {
      wmemmove (matrixp, matrixp + amt, w - amt);
      matrixp += screen->width;
    }
  screen_fill (screen, x + w - amt, y, amt, h, chr, attr);
}

static void
screen_scroll_right (screen_t screen, size_t x, size_t y, size_t w, size_t h,
		     int amt, wchar_t chr, char attr)
{
  int i;
  wchar_t *matrixp = screen->matrix
    + ((screen->current_line + y) % screen->height) * screen->width + x;

  if (amt < 0)
    return;
  if (amt > w)
    amt = w;

  for (i = 0; i < y + h; i++)
    {
      wmemmove (matrixp + amt, matrixp, w - amt);
      matrixp += screen->width;
    }
  screen_fill (screen, x, y, amt, h, chr, attr);
}


static error_t
output_init (output_t output, const char *encoding)
{
  condition_init (&output->resumed);
  output->stopped = 0;
  output->buffer = NULL;
  output->allocated = 0;
  output->size = 0;

  /* WCHAR_T happens to be UCS-4 on the GNU system.  */
  output->cd = iconv_open ("WCHAR_T", encoding);
  if (output->cd == (iconv_t) -1)
    return errno;
  return 0;
}

static void
output_deinit (output_t output)
{
  iconv_close (output->cd);
}


static void
handle_esc_bracket_hl (cursor_t cursor, int code, int flag)
{
  switch (code)
    {
    case 34:
      /* Cursor standout: <cnorm>, <cvvis>.  */
      if (flag)
	cursor->status |= CURSOR_STANDOUT;
      else
	cursor->status &= ~CURSOR_STANDOUT;
      /* XXX Flag cursor status change.  */
      break;
    }
}

static void
handle_esc_bracket_m (attr_t attr, int code)
{
  switch (code)
    {
    case 0:
      /* All attributes off: <sgr0>.  */
      attr->fg = attr->def_fg;
      attr->bg = attr->def_bg;
      attr->reverse = attr->bold = attr->blink
	= attr->invisible = attr->dim
	= attr->underline = 0;
      /* Cursor attributes aren't text attributes.  */
      break;
    case 1:
      /* Bold on: <bold>.  */
      attr->bold = 1;
      break;
    case 2:
      /* Dim on: <dim>.  */
      attr->dim = 1;
      break;
    case 4:
      /* Underline on: <smul>.  */
      attr->underline = 1;
      break;
    case 5:
      /* Blink on: <blink>.  */
      attr->blink = 1;
      break;
    case 7:
      /* Reverse video on: <rev>, <smso>.  */
      attr->reverse = 1;
      break;
    case 8:
      /* Concealed on: <invis>.  */
      attr->invisible = 1;
      break;
    case 21:
      /* Bold Off.  */
      attr->bold = 0;
      break;
    case 22:
      /* Dim off.  */
      attr->dim = 0;
      break;
    case 24:
      /* Underline off: <rmul>.  */
      attr->underline = 0;
      break;
    case 25:
      /* Blink off.  */
      attr->blink = 0;
      break;
    case 27:
      /* Reverse video off: <rmso>.  */
      attr->reverse = 0;
      break;
    case 28:
      /* Concealed off.  */
      attr->invisible = 0;
      break;
    case 30 ... 37:
      /* Set foreground color: <setaf>.  */
      attr->fg = code - 30;
      break;
    case 39:
      /* Default foreground color; ANSI?.  */
      attr->fg = attr->def_fg;
      break;
    case 40 ... 47:
      /* Set background color: <setab>.  */
      attr->bg = code - 40;
      break;
    case 49:
      /* Default background color; ANSI?.  */
      attr->bg = attr->def_bg;
      break;
    }
  /* XXX */
  /* recalc_attr (display); */
}

static void
handle_esc_bracket (display_t display, char op)
{
  parse_t parse = &display->output.parse;
  int i;

  static void limit_cursor (void)
    {
      if (display->cursor.x >= display->screen.width)
	display->cursor.x = display->screen.width - 1;
      else if (display->cursor.x < 0)
	display->cursor.x = 0;
      
      if (display->cursor.y >= display->screen.height)
	display->cursor.y = display->screen.height - 1;
      else if (display->cursor.y < 0)
	display->cursor.y = 0;

      /* XXX Flag cursor change.  */
    }

  switch (op)
    {
    case 'H':
    case 'f':
      /* Cursor position: <cup>.  */
      display->cursor.x = parse->params[1] - 1;
      display->cursor.y = parse->params[0] - 1;
      limit_cursor ();
      break;
    case 'G':
      /* Horizontal position: <hpa>.  */
      display->cursor.x = parse->params[0] - 1;
      limit_cursor ();
      break;
    case 'F':
      /* Beginning of previous line.  */
      display->cursor.x = 0;
      /* fall through */
    case 'A':
      /* Cursor up: <cuu>, <cuu1>.  */
      display->cursor.y -= (parse->params[0] ?: 1);
      limit_cursor ();
      break;
    case 'E':
      /* Beginning of next line.  */
      display->cursor.x = 0;
      /* Fall through.  */
    case 'B':
      /* Cursor down: <cud1>, <cud>.  */
      display->cursor.y += (parse->params[0] ?: 1);
      limit_cursor ();
      break;
    case 'C':
      /* Cursor right: <cuf1>, <cuf>.  */
      display->cursor.x += (parse->params[0] ?: 1);
      limit_cursor ();
      break;
    case 'D':
      /* Cursor left: <cub>, <cub1>.  */
      display->cursor.x -= (parse->params[0] ?: 1);
      limit_cursor ();
      break;
    case 's':
      /* Save cursor position: <sc>.  */
      display->cursor.saved_x = display->cursor.x;
      display->cursor.saved_y = display->cursor.y;
      break;
    case 'u':
      /* Restore cursor position: <rc>.  */
      display->cursor.x = display->cursor.saved_x;
      display->cursor.y = display->cursor.saved_y;
      /* In case the screen was larger before:  */
      limit_cursor ();
      break;
    case 'h':
      /* Reset mode.  */
      for (i = 0; i < parse->nparams; i++)
	handle_esc_bracket_hl (&display->cursor, parse->params[i], 0);
      break;
    case 'l':
      /* Set mode.  */
      for (i = 0; i < parse->nparams; i++)
	handle_esc_bracket_hl (&display->cursor, parse->params[i], 1);
      break;
    case 'm':
      for (i = 0; i < parse->nparams; i++)
	handle_esc_bracket_m (&display->attr, parse->params[i]);
      break;
    case 'J':
      switch (parse->params[0])
	{
	case 0:
	  /* Clear to end of screen: <ed>.  */
	  screen_fill (&display->screen, display->cursor.x, display->cursor.y,
		       display->screen.width - display->cursor.x, 1, L' ',
		       display->attr.current);
	  screen_fill (&display->screen, 0, display->cursor.y + 1,
		       display->screen.width,
		       display->screen.height - display->cursor.y,
			L' ', display->attr.current);
	  break;
	case 1:
	  /* Clear to beginning of screen.  */
	  screen_fill (&display->screen, 0, 0,
		       display->screen.width, display->cursor.y,
		       L' ', display->attr.current);
	  screen_fill (&display->screen, 0, display->cursor.y,
		       display->cursor.x + 1, 1,
		       L' ', display->attr.current);
	  break;
	case 2:
	  /* Clear entire screen.  */
	  screen_fill (&display->screen, 0, 0,
		       display->screen.width, display->screen.height,
		       L' ', display->attr.current);
	  break;
	}
      break;
    case 'K':
      switch (parse->params[0])
	{
	case 0:
	  /* Clear to end of line: <el>.  */
	  screen_fill (&display->screen, display->cursor.x, display->cursor.y,
		       display->screen.width - display->cursor.x, 1,
		       L' ', display->attr.current);
	  break;
	case 1:
	  /* Clear to beginning of line: <el1>.  */
	  screen_fill (&display->screen, 0, display->cursor.y,
		       display->cursor.x + 1, 1,
		       L' ', display->attr.current);
	  break;
	case 2:
	  /* Clear entire line.  */
	  screen_fill (&display->screen, 0, display->cursor.y,
		       display->screen.width, 1,
		       L' ', display->attr.current);
	  break;
	}
      break;
    case 'L':
      /* Insert line(s): <il1>, <il>.  */
      screen_scroll_down (&display->screen, 0, display->cursor.y,
			  display->screen.width,
			  display->screen.height - display->cursor.y,
			  parse->params[0] ?: 1,
			  L' ', display->attr.current);
      break;
    case 'M':
      /* Delete line(s): <dl1>, <dl>.  */
      screen_scroll_up (&display->screen, 0, display->cursor.y,
			display->screen.width,
			display->screen.height - display->cursor.y,
			parse->params[0] ?: 1,
			L' ', display->attr.current);
      break;
    case '@':
      /* Insert character(s): <ich1>, <ich>.  */
      screen_scroll_right (&display->screen, display->cursor.x,
			   display->cursor.y,
			   display->screen.width - display->cursor.x, 1,
			   parse->params[0] ?: 1,
			   L' ', display->attr.current);
      break;
    case 'P':
      /* Delete character(s): <dch1>, <dch>.  */
      screen_scroll_left (&display->screen, display->cursor.x,
			  display->cursor.y,
			  display->screen.width - display->cursor.x, 1,
			  parse->params[0] ?: 1,
			  L' ', display->attr.current);
      break;
    case 'S':
      /* Scroll up: <ind>, <indn>.  */
      screen_scroll_up (&display->screen, 0, 0,
			display->screen.width, display->screen.height,
			parse->params[0] ?: 1,
			L' ', display->attr.current);
      break;
    case 'T':
      /* Scroll down: <ri>, <rin>.  */
      screen_scroll_down (&display->screen, 0, 0,
			  display->screen.width, display->screen.height,
			  parse->params[0] ?: 1,
			  L' ', display->attr.current);
      break;
    case 'X':
      /* Erase character(s): <ech>.  */
      screen_fill (&display->screen, display->cursor.x, display->cursor.y,
		   parse->params[0] ?: 1, 1,
		   L' ', display->attr.current);
      break;
    }
}

static void
handle_esc_bracket_question_hl (display_t display, int code, int flag)
{
  switch (code)
    {
    case 25:
      /* Cursor invisibility: <civis>, <cnorm>.  */
      if (flag)
	display->cursor.status |= CURSOR_INVISIBLE;
      else
	display->cursor.status &= ~CURSOR_INVISIBLE;
      /* XXX Flag cursor status change.  */
      break;
    }
}


static void
handle_esc_bracket_question (display_t display, char op)
{
  parse_t parse = &display->output.parse;

  int i;
  switch (op)
    {
    case 'h':
      /* Reset mode.  */
      for (i = 0; i < parse->nparams; ++i)
	handle_esc_bracket_question_hl (display, parse->params[i], 0);
      break;
    case 'l':
      /* Set mode.  */
      for (i = 0; i < parse->nparams; ++i)
	handle_esc_bracket_question_hl (display, parse->params[i], 1);
      break;
    }
}

/* Display must be locked.  */
static void
display_output_one (display_t display, wchar_t chr)
{
  parse_t parse = &display->output.parse;

  void newline (void)
    {
      if (display->cursor.y < display->screen.height - 1)
	{
	  display->cursor.y++;
	  /* XXX Flag cursor update.  */
	}
      else
	{
	  display->screen.current_line++;
	  display->screen.current_line %= display->screen.lines;

	  /* XXX Set attribute flags.  */
	  screen_fill (&display->screen, 0, display->screen.height - 1,
		       display->screen.width, 1, L' ', display->screen.width);
	  if (display->screen.scrolling_max <
	      display->screen.lines - display->screen.height)
	    display->screen.scrolling_max++;
	  /* XXX Flag current line change.  */
	  /* XXX Flag change of last line.  */
	  /* XXX Possibly flag change of length of scroll back buffer.  */
	}
    }

  switch (parse->state)
    {
    case STATE_NORMAL:
      switch (chr)
	{
	case L'\r':
	  /* Carriage return: <cr>.  */
	  if (display->cursor.x)
	    {
	      display->cursor.x = 0;
	      /* XXX Flag cursor update.  */
	    }
	  break;
	case L'\n':
	  /* Cursor down: <cud1>, scroll up: <ind>.  */
	  newline ();
	  break;
	case L'\b':
	  /* Cursor backward: <cub1>.  */
	  if (display->cursor.x > 0 || display->cursor.y > 0)
	    {
	      if (display->cursor.x > 0)
		display->cursor.x--;
	      else
		{
		  /* XXX This implements the <bw> functionality.
		     The alternative is to cut off and set x to 0.  */
		  display->cursor.x = display->screen.width - 1;
		  display->cursor.y--;
		}
	      /* XXX Flag cursor update.  */
	    }
	  break;
	case L'\t':
	  /* Horizontal tab: <ht> */
	  display->cursor.x = (display->cursor.x | 7) + 1;
	  if (display->cursor.x >= display->screen.width)
	    {
	      display->cursor.x = 0;
	      newline ();
	    }
	  /* XXX Flag cursor update.  */
	  break;
	case L'\033':
	  parse->state = STATE_ESC;
	  break;
	case L'\0':
	  /* Padding character: <pad>.  */
	  break;
	default:
	  {
	    int line = (display->screen.current_line + display->cursor.y)
	      % display->screen.lines;

	    /* XXX Set attribute flags.  */
	    display->screen.matrix[line * display->screen.width
				   + display->cursor.x] = chr;

	    display->cursor.x++;
	    if (display->cursor.x == display->screen.width)
	      {
		display->cursor.x = 0;
		newline ();
	      }
	  }
	  break;
	}
      break;

    case STATE_ESC:
      switch (chr)
	{
	case L'[':
	  parse->state = STATE_ESC_BRACKET_INIT;
	  break;
	case L'c':
	  /* Clear screen and home cursor: <clear>.  */
	  screen_fill (&display->screen, 0, 0,
		       display->screen.width, display->screen.height,
		       L' ', display->attr.current);
	  display->cursor.x = display->cursor.y = 0;
	  /* XXX Flag cursor change.  */
	  parse->state = STATE_NORMAL;
	  break;
	default:
	  /* Unsupported escape sequence.  */
	  parse->state = STATE_NORMAL;
	  break;
	}
      break;
      
    case STATE_ESC_BRACKET_INIT:
      memset (&parse->params, 0, sizeof parse->params);
      parse->nparams = 0;
      if (chr == '?')
	{
	  parse->state = STATE_ESC_BRACKET_QUESTION;
	  break;	/* Consume the question mark.  */
	}
      else
	parse->state = STATE_ESC_BRACKET;
      /* Fall through.  */
    case STATE_ESC_BRACKET:
    case STATE_ESC_BRACKET_QUESTION:
      if (chr >= '0' && chr <= '9')
	parse->params[parse->nparams]
	    = parse->params[parse->nparams]*10 + chr - '0';
      else if (chr == ';')
	{
	  if (++(parse->nparams) >= PARSE_MAX_PARAMS)
	    parse->state = STATE_NORMAL; /* too many */
	}
      else
	{
	  parse->nparams++;
	  if (parse->state == STATE_ESC_BRACKET)
	    handle_esc_bracket (display, chr);
	  else
	    handle_esc_bracket_question (display, chr);
	  parse->state = STATE_NORMAL;
	}
      break;
    default:
      abort ();
    }
}

/* Output LENGTH bytes starting from BUFFER in the system encoding.
   Set BUFFER and LENGTH to the new values.  The exact semantics are
   just as in the iconv interface.  */
static error_t
display_output_some (display_t display, char **buffer, size_t *length)
{
#define CONV_OUTBUF_SIZE 256
  error_t err = 0;

  while (!err && *length > 0)
    {
      size_t nconv;
      wchar_t outbuf[CONV_OUTBUF_SIZE];
      char *outptr = (char *) outbuf;
      size_t outsize = CONV_OUTBUF_SIZE * sizeof (wchar_t);
      error_t saved_err;
      int i;

      nconv = iconv (display->output.cd, buffer, length, &outptr, &outsize);
      saved_err = errno;

      /* First process all successfully converted characters.  */
      for (i = 0; i < CONV_OUTBUF_SIZE - outsize / sizeof (wchar_t); i++)
	display_output_one (display, outbuf[i]);

      if (nconv == (size_t) -1)
	{
	  /* Conversion didn't work out.  */
	  if (saved_err == EINVAL)
	    /* This is only an unfinished byte sequence at the end of
	       the input buffer.  */
	    break;
	  else if (saved_err != E2BIG)
	    err = saved_err;
	}
    }
  return err;
}

/* Create a new virtual console display, with the system encoding
   being ENCODING.  */
error_t
display_create (display_t *r_display, const char *encoding)
{
  error_t err = 0;
  display_t display;

  *r_display = NULL;
  display = calloc (1, sizeof *display);
  if (!display)
    return ENOMEM;

  mutex_init (&display->lock);
  err = screen_init (&display->screen);
  if (err)
    {
      free (display);
      return err;
    }

  err = output_init (&display->output, encoding);
  if (err)
    {
      screen_deinit (&display->screen);
      free (display);
    }
  *r_display = display;
  return err;
}


/* Destroy the display DISPLAY.  */
void
display_destroy (display_t display)
{
  output_deinit (&display->output);
  screen_deinit (&display->screen);
  free (display);
}


/* Return the dimensions of the display DISPLAY in *WINSIZE.  */
void
display_getsize (display_t display, struct winsize *winsize)
{
  mutex_lock (&display->lock);
  winsize->ws_row = display->screen.height;
  winsize->ws_col = display->screen.width;
  winsize->ws_xpixel = 0;
  winsize->ws_ypixel = 0;
  mutex_unlock (&display->lock);
}


/* Set the owner of the display DISPLAY to PID.  The owner receives
   the SIGWINCH signal when the terminal size changes.  */
error_t
display_set_owner (display_t display, pid_t pid)
{
  mutex_lock (&display->lock);
  display->has_owner = 1;
  display->owner_id = pid;
  mutex_unlock (&display->lock);
  return 0;
}


/* Return the owner of the display DISPLAY in PID.  If there is no
   owner, return ENOTTY.  */
error_t
display_get_owner (display_t display, pid_t *pid)
{
  error_t err = 0;
  mutex_lock (&display->lock);
  if (!display->has_owner)
    err = ENOTTY;
  else
    *pid = display->owner_id;
  mutex_unlock (&display->lock);
  return err;
}

/* Output DATALEN characters from the buffer DATA on display DISPLAY.
   The DATA must be supplied in the system encoding configured for
   DISPLAY.  The function returns the amount of bytes written (might
   be smaller than DATALEN) or -1 and the error number in errno.  If
   NONBLOCK is not zero, return with -1 and set errno to EWOULDBLOCK
   if operation would block for a long time.  */
ssize_t
display_output (display_t display, int nonblock, char *data, size_t datalen)
{
  output_t output = &display->output;
  error_t err;
  char *buffer;
  size_t buffer_size;
  ssize_t amount;

  error_t ensure_output_buffer_size (size_t new_size)
    {
      /* Must be a power of two.  */
#define OUTPUT_ALLOCSIZE 32

      if (output->allocated < new_size)
	{
	  char *new_buffer;
	  new_size = (new_size + OUTPUT_ALLOCSIZE - 1)
	    & ~(OUTPUT_ALLOCSIZE - 1);
	  new_buffer = realloc (output->buffer, new_size);
	  if (!new_buffer)
	    return ENOMEM;
	  output->buffer = new_buffer;
	  output->allocated = new_size;
	}
      return 0;
    }

  mutex_lock (&display->lock);
  while (output->stopped)
    {
      if (nonblock)
        {
          mutex_unlock (&display->lock);
          errno = EWOULDBLOCK;
          return -1;
        }
      if (hurd_condition_wait (&output->resumed, &display->lock))
        {
          mutex_unlock (&display->lock);
          errno = EINTR;
          return -1;
        }
    }

  if (output->size)
    {
      err = ensure_output_buffer_size (output->size + datalen);
      if (err)
        {
          mutex_unlock (&display->lock);
          errno = ENOMEM;
          return -1;
        }
      buffer = output->buffer;
      buffer_size = output->size;
      memcpy (buffer + buffer_size, data, datalen);
      buffer_size += datalen;
    }
  else
    {
      buffer = data;
      buffer_size = datalen;
    }
  amount = buffer_size;
  err = display_output_some (display, &buffer, &buffer_size);
  amount -= buffer_size;

  if (err && !amount)
    {
      mutex_unlock (&display->lock);
      errno = err;
      return err;
    }
  /* XXX What should be done with invalid characters etc?  */
  if (buffer_size)
    {
      /* If we used the caller's buffer DATA, the remaining bytes
         might not fit in our internal output buffer.  In this case we
         can reallocate the buffer in VCONS without needing to update
         OUTPUT (as it points into DATA). */
      err = ensure_output_buffer_size (buffer_size);
      if (err)
        {
          mutex_unlock (&display->lock);
          return err;
        }
      memmove (output->buffer, buffer, buffer_size);
    }
  output->size = buffer_size;
  amount += buffer_size;

  mutex_unlock (&display->lock);
  return amount;
}

ssize_t display_read (display_t display, int nonblock, off_t off,
		      char *data, size_t len)
{
  u_int32_t metadata[8];
  size_t metadatalen = sizeof (metadata);
  ssize_t written = 0;

  mutex_lock (&display->lock);
  metadata[0] = display->screen.width;
  metadata[1] = display->screen.height;
  metadata[2] = display->screen.lines;
  metadata[3] = display->screen.current_line;
  metadata[4] = display->screen.scrolling_max;
  metadata[5] = display->cursor.x;
  metadata[6] = display->cursor.y;
  metadata[7] = display->cursor.status;
  
  if (off >= 0 && off < metadatalen)
    {
      int part_len = len;

      if (part_len > metadatalen)
	part_len = metadatalen;
      memcpy (data, (char *) metadata + off, part_len);
      data += part_len;
      len -= part_len;
      written += part_len;
    }
  off -= metadatalen;
  if (off < 0)
    off = 0;
  
  if (off + len > 2000 * sizeof(wchar_t))
    len = 2000 * sizeof(wchar_t) - off;
  memcpy (data, (char *) display->screen.matrix + off, len);
  mutex_unlock (&display->lock);
  return written + len;
}

/* Resume the output on the display DISPLAY.  */
void
display_start_output (display_t display)
{
  mutex_lock (&display->lock);
  if (display->output.stopped)
    {
      display->output.stopped = 0;
      condition_broadcast (&display->output.resumed);
    }
  mutex_unlock (&display->lock);
}


/* Stop all output on the display DISPLAY.  */
void
display_stop_output (display_t display)
{
  mutex_lock (&display->lock);
  display->output.stopped = 1;
  mutex_unlock (&display->lock);
}


/* Return the number of pending output bytes for DISPLAY.  */
size_t
display_pending_output (display_t display)
{
  int output_size;
  mutex_lock (&display->lock);
  output_size = display->output.size;
  mutex_unlock (&display->lock);
  return output_size;
}


/* Flush the output buffer, discarding all pending data.  */
void
display_discard_output (display_t display)
{
  mutex_lock (&display->lock);
  display->output.size = 0;
  mutex_unlock (&display->lock);
}